In the field of digital radiography a wide variety of image acquisition techniques have been developed such as computerised tomography, nuclear magnetic resonance, ultrasound, detection of a radiation image by means of a CCD sensor or a video camera, radiographic film scanning etc.
Still another technique has been developed wherein a radiation imager for example x-rays transmitted by an object, is stored in a screen comprising a photostimulable phosphor such as one of the phosphors described in European patent application 503 702 published and in U.S. Ser. No. 07/842,603, now U.S. Pat. No. 5,340,661.
The technique for reading out the stored radiation image consists of scanning the screen with stimulating radiation, such as laser light of the appropriate wavelength, detecting the light emitted upon stimulation and converting the emitted light into an electric representation for example by means of a photomultiplier. This technique further comprises digitizing and processing said electric signal and applying it to a recorder for recording a hard copy for example on film. This hard-copy can be viewed on a lightbox for diagnosic purposes.
After read-out of the image stored in the photostimulable phosphor screen one disposes of an electric image representation that can be applied to a monitor for display of the corresponding visual image.
Apparatus for performing the above-described image acquisition methods are commonly accompanied by a preview monitor to which the image signal is applied before being sent to an output device, i.e. a recorder or a workstation.
The image can be then be evaluated either on the recorded hard-copy or on the display unit of the workstation or on the preview monitor.
However, before the image is available at the output of the hard copy recorder, some time passes due to the duration of the recording process including the development of the film and occacionally due to formation of a queue of image signals waiting to be reproduced by the recorder.
Also when the image is shown and evaluated at the workstation some processing time is to be taken into account before the visible image is available.
Inspection on the preview monitor on the other hand can be performed almost immediately after acquisition and hence provides for early feedback to the operator so that corrections can be performed in case the acquisition went wrong.
In hospitals that dispose of several radiology rooms it is possible that a preview monitor is installed in each radiology room in addition to a central preview monitor that is provided in the vicinity of an image acquisition apparatus.
Immediately following acquisition, the acquired image is shown on the central monitor and eventually also on monitors that are locally provided in the radiology rooms so that the evaluation can be made by the operator who is occupied in each of the rooms. Evaluation can be made very fast after image acquisition so that in case of mis-acquisition the error can be immediately corrected.
Sequentially acquired images are sequentially shown on the monitor(s). This mode of operation allows fast evaluation but has the disadvantage that the period of time of which the operator disposes to make an evaluation depends on the period of time between the display of a first image and the moment on which data regarding a subsequent image are available. Typically this is for example in a system wherein an image is read-out from a photostimulable phosphor screen about 1 minute. So, it may happen that an image is already removed from the display and a subsequent image is displayed while the operator did not yet have the opportunity to evaluate the former image on the display unit.
This problem is partially solved by providing the acquisition apparatus with an interaction modality for example implemented by a wait, cancel and proceed function. Upon activation of the wait function for example in a system wherein images are stored in photostimulable phosphor screens, the operator can interrupt the process of successively reading out a sequence of phosphor screens so that he can study and evaluate a read out image on the preview monitor until he activates the cancel or proceed function.
Upon activation of the proceed function the acquired image signal is sent further to the output device whereas upon activation of the cancel function, the image signal is no longer retained. After activation of either of these functions, the interruption is terminated and the acquisition apparatus starts acquiring a next image.
By using these functions the operator can dispose of a longer period of time to make a first evaluation on the preview monitor. However, this procedure decreases the throughput of the read-out apparatus.
In case more than one monitor is provided and every acquired image is sent to each of the monitors, it may occur that an operator who is occupied in one radiology room and makes his evaluation on the locally provided monitor needs to let pass the images taken in other rooms. Since these images are of no interest to him, this brings about a waste of time and even demands from the operator increased attention to detect among the displayed images those images made in the radiology room of interest.
U.S. Pat. No. 5,015,854 issued May 14, 1991 discloses a configuration of a workstation (not preview monitor) to be interfaced with a signal gathering apparatus.
The disclosure deals in particular with the retrieval of particular images out of said large number of images stored in a storage device.
The retrieval is performed with the aid of outline images.
When a stored image is to be retrieved by the operator of the workstation, a number of outline images is displayed simultaneously on the display device so that the operator can select the image of interest on the basis of low detailed pictorial information displayed on the monitor screen. On the basis of this selection he can order display of the complete non-reduced image.
This method is generally referred to as "pictorial index" and has been described extensively by Th. Wendler et al. in Pictorial Information Systems in Medicine, published in Nato ASI Series, Vol. F19.